1. Field
The present disclosure relates to an iodine absorbent material containing a salt, and a radioactive iodine removal system using the same, and more particularly, to an iodine absorbent material applicable when volatile fission products are abnormally emitted from nuclear facilities, and a radioactive iodine removal system using the same.
2. Discussion of Related Technology
Radioactive iodine (131I) is one of fission products formed as a fissile material undergoes nuclear fission, which is a radioactive isotope that accounts for approximately 2.8% of a total of fission products formed as uranium undergoes nuclear fission by means of thermal neutrons (fission yield: 2.8%). The molecular iodine of this element has a high level of radioactivity and exists as gas, and thus, the absorptiveness in human body by respiration is high, therefore is a nuclide whose initial spread is of particular concern when a nuclear accident takes place.
In general, iodine is present in the form of cesium iodide (CsI) in a spent nuclear fuel, and released to the outside in the CsI form. Since there is a high possibility that the first exposed environment would be the inner part of a coolant, a method of suppressing an oxidation reaction of iodide (I−) into iodine (I2). The released iodide (I−) ion is stably dissolved in the coolant, but the molecular iodine (I2) is volatile. In this background, a method of controlling a pH value of a coolant and redox conditions has been used for a long period of time. A level of volatility of the iodine present in an aqueous solution may be lowered by controlling the pH value of the coolant and the redox conditions as described above. However, the iodine is released into an internal atmosphere of a reactor containment building due to an increase in temperature of the coolant, or an increase in a level of volatility of the iodine under an environment exposed to radiation. Also, since the iodine easily reacts with organic compounds and increase a level of volatility while forming organic iodide, methods of minimizing contact with an organic compound have been used.
In general, a method of removing iodine released in the atmosphere includes a method using an absorbent material. A representative absorbent material includes a carbon-based absorbent material such as activated carbon (i.e., charcoal), and a silver.
J. G. Jolley and H. G. Tompkins from the US Idaho Falls Institute evaluated a level of absorption of various organic iodines at room temperature and a high-temperature desorption characteristic using silver zeolite. Also, H. Faghihian et al. (J. Radioanalytical and Nuclear Chemistry, (2002) 254: 545-550) disclosed that two kinds of natural zeolites (clinoptilolite and natrolite) may be used as a radioactive iodine absorbent by measuring a level of absorption of radioactive iodine into both of the natural zeolites. Japanese Patent Application Publication No. 2003-302493 (Oct. 24, 2003) discloses a method of fixing radioactive iodine gas using a silicate-based mineral having micropores, and Japanese Patent Application Publication No. Hei 5-126995 (May 25, 1993) discloses a method of separating an iodine species by precipitation by treating waste water containing radioactive iodine with silver nitrate. Also, Korean Patent Application Publication No. 2000-0008867 (Feb. 15, 2000) discloses a method of converting a chemical species of radioactive iodine in an aqueous solution or waste water into molecular iodine (I2) to remove the chemical species from a gaseous phase to activated carbon.
As one of representative absorbent materials, a silver-based radioactive iodine absorbent material has two limits. First, since silver belongs to the group of noble metals, an absorbent material using silver is very expensive compared with its effects. Second, silver has high reactivity with iodine, but also exhibits high reactivity with chloride ions. Since many nuclear power plants are generally installed on the seashore, and salt aerosol is present at a high concentration in the atmosphere within several kilometers from the seashore. Accordingly, absorption performance of the silver-based absorbent material in a seashore region may be degraded. Also, performance of the carbon-based absorbent material may be degraded when other materials such as moisture are present in the atmosphere. The above-described methods known in the related art are effective when iodine is present in a high concentration in a closed space. However, once the iodine is released into the atmosphere and is mixed with a large amount of moisture and salt, decontamination efficiency is significantly degraded using the current capture method.
The foregoing discussion is to provide general background information, and does not constitute an admission of the prior art.